Deep-draw forming methods include spinning, press working and hydraulic forming.
In spinning, a blank is placed on a rotary forming die and then pressed against it using a spinning bar to a deep-drawn form.
In press working, a blank is pressed in a die (upper die, lower die) into a deep-drawn form. Under some conditions, the forming is divided into several steps.
There is another method of deep drawing through two processes of spinning and press working.
For example, manufacturing of cooking bowls in a D shape is performed through two processes of spinning and press working. Specifically, a blank is worked into a hemispherical shape by spinning, and then a part of the side surface of the hemispherical formed product is formed flat by press working to produce a D shape, which method is disclosed in Japanese Patent Laid-Open Publication No. HEI-7-308724. This D-shaped container manufacturing method will be described with reference to FIG. 15 hereof.
Referring to FIG. 15, in the conventional D-shaped container manufacturing method, first, a thin blank sheet is deep-draw formed by spinning to produce a hemispherical container 200. Then, the hemispherical container 200 is placed on a first die 211 of a press working device 210, and the side surface 201 of the hemispherical container 200 is partially pressed from the side as shown by arrow (a) into a flat shape using a second die 212, whereby to produce a D-shaped bowl form with the flatly crushed portion. Thus enabled is the production of a D-shaped container from a thin material.
Although the above manufacturing method enables deep-draw forming through spinning and subsequent press working, it is a manufacturing method only for D-shaped containers, and is not suitable for forming different shapes than bowl shapes. Different products require different numbers of drawing steps and different dies, resulting in different process steps suitable for the respective different products. If it is possible to previously spin form a shape which prevents fracture and wrinkling in final press working, the effects of spinning such as reduction in die cost can be obtained.
It is thus desired to be able to form an elliptic deep-drawn product of a U-shaped cross section in two processes of a spinning process and a press working process, so as to reduce production costs even in small-quantity production.